Fix InstCombine address space assert

Workaround bug where the InstCombine pass was asserting on the IR added in lit
test, where we have a bitcast instruction after a GEP from an addrspace cast.

The second bitcast in the test was getting combined into
`bitcast <16 x i32>* %0 to <16 x i32> addrspace(3)*`, which looks like it should
be an addrspace cast instruction instead. Otherwise if control flow is allowed
to continue as it is now we create a GEP instruction
`<badref> = getelementptr inbounds <16 x i32>, <16 x i32>* %0, i32 0`. However
because the type of this instruction doesn't match the address space we hit an
assert when replacing the bitcast with that GEP.

```
void llvm::Value::doRAUW(llvm::Value*, bool): Assertion `New->getType() == getType() && "replaceAllUses of value with new value of different type!"' failed.
```

Differential Revision: https://reviews.llvm.org/D50058

llvm-svn: 338395

Author: EwanC

llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp

@@ -2243,6 +2243,12 @@ Instruction *InstCombiner::visitBitCast(BitCastInst &CI) {
     Type *DstElTy = DstPTy->getElementType();
     Type *SrcElTy = SrcPTy->getElementType();
 
+    // Casting pointers between the same type, but with different address spaces
+    // is an addrspace cast rather than a bitcast.
+    if ((DstElTy == SrcElTy) &&
+        (DstPTy->getAddressSpace() != SrcPTy->getAddressSpace()))
+      return new AddrSpaceCastInst(Src, DestTy);
+
     // If we are casting a alloca to a pointer to a type of the same
     // size, rewrite the allocation instruction to allocate the "right" type.
     // There is no need to modify malloc calls because it is their bitcast that

llvm/test/Transforms/InstCombine/gep-addrspace.ll

@@ -65,3 +65,22 @@ define { i8, i8 } @inbounds_after_addrspacecast() {
   ret { i8, i8 } %insert
 }
 
+
+declare spir_func <16 x i32> @my_extern_func()
+
+; check that a bitcast is not generated when we need an addrspace cast
+define void @bitcast_after_gep(<16 x i32>* %t0) {
+; CHECK-LABEL: @bitcast_after_gep(
+; CHECK-NEXT:    [[T4:%.*]] = addrspacecast <16 x i32>* [[T0:%.*]] to <16 x i32> addrspace(3)*
+; CHECK-NEXT:    [[CALL:%.*]] = call spir_func <16 x i32> @my_extern_func()
+; CHECK-NEXT:    store <16 x i32> [[CALL]], <16 x i32> addrspace(3)* [[T4]], align 64
+; CHECK-NEXT:    ret void
+;
+  %t1 = bitcast <16 x i32>* %t0 to [16 x i32]*
+  %t2 = addrspacecast [16 x i32]* %t1 to [16 x i32] addrspace(3)*
+  %t3 = getelementptr inbounds [16 x i32], [16 x i32] addrspace(3)* %t2, i64 0, i64 0
+  %t4 = bitcast i32 addrspace(3)* %t3 to <16 x i32> addrspace(3)*
+  %call = call spir_func <16 x i32> @my_extern_func()
+  store <16 x i32> %call, <16 x i32> addrspace(3)* %t4
+  ret void
+}